An electrocardiogram (ECG) is a tool used by physicians to diagnose heart problems and other potential health concerns. A full 12-lead ECG provides a multi-vector snapshot of heart function, typically recorded over 12 seconds, that can help diagnose rate and regularity of heartbeats, effect of drugs or cardiac devices, including pacemakers and implantable cardioverter-defibrillators (ICDs), and whether a patient has heart disease of any sort. Full 12-lead ECGs are used in-clinics or hospitals and, as a result, are limited to recording only those heart-related aspects present at the time of recording. Sporadic conditions that may not show up during a 12-second ECG recording require other means to diagnose them. These sporadic conditions include fainting or syncope; rhythm disorders, such as tachyarrhythmias and bradyarrhythmias; apneic episodes; and other cardiac and related disorders. Thus, a 12-lead ECG only provides a partial picture and can be insufficient for complete patient diagnosis of many cardiac disorders.
Diagnostic efficacy of problems, like syncope or cardiac arrhythmias, can be improved through the use of long-term extended wear ECG monitoring. Recording sufficient ECG and related physiological data over an extended period of time remains a significant challenge to healthcare providers, despite over a 40-year history of such efforts. Extended period monitoring essentially enables a physician to identify cardiac conditions, specifically, rhythm disorders, and other physiological events of potential concern. A 30-day observation day period is considered the “gold standard” of ECG monitoring, yet achieving a 30-day observation day period has heretofore proven unworkable because such ECG monitoring systems are arduous to employ, cumbersome to the patient, and excessively costly to manufacture and deploy. Nevertheless, if a patient's ECG could be recorded in an ambulatory setting over prolonged time periods, thereby allowing the patient to engage in activities of daily living, the chances of acquiring meaningful medical information and capturing an abnormal event while the patient is engaged in normal activities becomes more likely to be achieved.
Conventionally, maintaining continual contact between ECG electrodes and the skin after a day or two has been a problem. Time, dirt, moisture, and other environmental contaminants, as well as perspiration, skin oil, and dead skin cells from the patient's body, can get between an ECG electrode's non-conductive adhesive and the skin's surface. All of these factors adversely affect electrode adhesion and the quality of cardiac signal recordings. Furthermore, the physical movements of the patient and their clothing impart various compressional, tensile, and torsional forces on the contact point of an ECG electrode, especially over long recording times, and an inflexibly fastened ECG electrode will be prone to becoming dislodged. Moreover, dislodgment may occur unbeknownst to the patient, making the ECG recordings worthless. Further, some patients may have skin that is susceptible to itching or irritation, and the wearing of ECG electrodes can aggravate such skin conditions. Thus, a patient may want or need to periodically remove or replace ECG electrodes during a long-term ECG monitoring period, whether to replace a dislodged electrode, reestablish better adhesion, alleviate itching or irritation, allow for cleansing of the skin, allow for showering and exercise, or for other purpose. Such replacement or slight alteration in electrode location actually facilitates the goal of recording the ECG signal for long periods of time.
In addition, the high cost of the patient-wearable components used to provide long-term extended ECG monitoring can negatively influence the availability and use of monitors. Ideally, disposable, single-use components, such as adhesive electrodes, should be low cost, while other components of higher complexity, particularly the electronics hardware that detects and records ECG and related physiology, may be of unavoidably higher cost. To a degree, costs can be balanced by designing higher complexity components to be re-usable, but when the total cost of a full ECG monitoring ensemble remains high, despite the utilization of re-usable parts, the number of monitors available for use by healthcare providers can be inhibited. Cost, then, becomes a barrier to entry, which, in turn, can hinder or prevent healthcare providers from obtaining the means with which to efficaciously identify the physiology underlying sporadic cardiac arrhythmic conditions and can ultimately contribute to a failure to make a proper and timely medical diagnosis.
Conventionally, Holter monitors are widely used for long-term extended ECG monitoring. Typically, they are often used for only 24-48 hours. A typical Holter monitor is a wearable and portable version of an ECG that include cables for each electrode placed on the skin and a separate battery-powered ECG recorder. The cable and electrode combination (or leads) are placed in the anterior thoracic region in a manner similar to what is done with an in-clinic standard ECG machine. The duration of a Holter monitoring recording depends on the sensing and storage capabilities of the monitor, as well as battery life. A “looping” Holter (or event) monitor can operate for a longer period of time by overwriting older ECG tracings, thence “recycling” storage in favor of extended operation, yet at the risk of losing event data. Although capable of extended ECG monitoring, Holter monitors are cumbersome, expensive and typically only available by medical prescription, which limits their usability. Further, the skill required to properly place the electrodes on the patient's chest hinders or precludes a patient from replacing or removing the precordial leads and usually involves moving the patient from the physician office to a specialized center within the hospital or clinic.
The ZIO XT Patch and ZIO Event Card devices, manufactured by iRhythm Tech., Inc., San Francisco, Calif., are wearable stick-on monitoring devices that are typically worn on the upper left pectoral region to respectively provide continuous and looping ECG recording. The location is used to simulate surgically implanted monitors. Both of these devices are prescription-only and for single patient use. The ZIO XT Patch device is limited to a 14-day monitoring period, while the electrodes only of the ZIO Event Card device can be worn for up to 30 days. The ZIO XT Patch device combines both electronic recordation components and physical electrodes into a unitary assembly that adheres to the patient's skin. The ZIO XT Patch device uses adhesive sufficiently strong to support the weight of both the monitor and the electrodes over an extended period of time and to resist disadherence from the patient's body, albeit at the cost of disallowing removal or relocation during the monitoring period. The ZIO Event Card device is a form of downsized Holter monitor with a recorder component that must be removed temporarily during baths or other activities that could damage the non-waterproof electronics. Both devices represent compromises between length of wear and quality of ECG monitoring, especially with respect to ease of long term use, female-friendly fit, and quality of cardiac electrical potential signals, especially atrial (P-wave) signals.
Therefore, a need remains for a low cost extended wear continuously recording ECG monitor practicably capable of being worn for a long period of time, especially in patient's whose breast anatomy can interfere with signal quality in both men and women and that is capable of recording atrial action potential signals reliably.